SAs are assigned in a range from 1 - 65501. SAs 0 and 65501 - 65535 are reserved. Source Addresses must be geographically unique, which means that within an agency they must be unique, and if they are used more than once, the networks that they exist on must be geographically unique so that there is no confusion about which location an ALERT2 message is generated. The combination of Agency and SA must be unique globally.